Sound film system



May 12, 1942. C; N. BA1-SEL 2,282,927

SOUND FILM SYS TEM Filed NOV. 22, 1940 Powe-R Suppl. y

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Patented May 12, 1.9.42

sonni FILM SYSTEM Cecil N. Batsel, North Hollywood, Calif., assignor to Radio Corporation' of America, a corporation oi Delaware Application November 22, 1940, Serial No. 366,589 (Llaims.A (Cl. 179-1003) This invention relates to motion picture sound apparatus and particularly to a sound lm reproducing system.

In the art of sound recording and reproduction, variations are frequently made between the original signal amplitudes and the recorded amplitudes, and also between the reproduced amplitudes and the recorded amplitudes. It is well known that the film sound track range is much the introduction of compression in the sound record during recording,

. 'I'he principal object of the invention, therefore, is to facilitate the amplitude control of a reproduced or recorded sound record.

Another object of the invention is to vary the amplitudes of a signal to or from a sound record. A further object of the invention is to increase the controllable range of sound reproduction less `than many signal ranges, such as those of an 10 rom a sound record without distortion. orchestra, and to record the entire signal range A further object of the invention is to utilize on the lm, compression is employed. This is an electron multiplier as a variable gain amaccomplished by decreasing the higher signal plifier for reproducing or recording a sound amplitudes to a certain degree before impresrecord. sion on the recordingv medium, the lower amplil5 Although the novel features which are betudes being decreased proportionately or in some lieved to be characteristic oi this invention will denite predetermined ratio. This method also be pointed outwith particularity in the apaccomplishes the reduction of ground noise since pended claims, the manner of its organization the lower amplitudes may be recorded at a reland the mode of its operation will'be better unativelyhigher level than would otherwise be posderstood by referring to the following descripsible. tion read in conjunction with the accompanying In the reproduction of a sound record which drawing forming a part thereof, in which the has been compressed tojany appreciable extent, single i'lgure is a schematic and diagrammatic the reverse of compression or expansion is rearrangement of a sound reproducing system quired in order to restore the respective ampliembodying the invention. y tudes of the signal to their original relationships. Referring to the drawing, a iilm 5 has posi- It is also desirable in many instances to expand tioned thereon a sound record S of either the a normal or linearly recorded signal to increase variable area or variable density type. Posithe dramatic eiect thereof. tioned within the area intermediate the sprocket Various types of compressors and expanders holes l and .longitudinally of the film 5 is a conare known in the art, the most successful at prestrol record 8, such a lcontrol record being disent being of the electronic type wherein the amclosed in copending U. S. application Serial No. pliiication factor of a vacuum tube is varied 181,634, filed December 24, 1937. The film 51S under control of the average amplitude variaadvanced through the reproducing apparatus in tions of the signal. By the use of a variable mu any suitable manner such that` it passes over a vacuum tube in the variable gain amplifier, a roller i0 anda roller ii. Light is passed through variation in amplication is obtainable without the sound record 6 as the film passes over the the introduction of any substantial distortion in roller i0, the light being generated from a the compressed or expanded signal. The pressource such as a lamp I4. The light is gathered ent invention is directed to an electronic type of by a collecting lens I5 projected on a slit mask variable gain amplifier which may be utilized for i6 having a slit il therein and then projected either compression or expansion, the device beon the sound track area ofthe ilm 5 by a lens ing thev electronic multiplier type -of tube which i9. The emergent light from 'the film is colcombines a photoelectric cell and amplifier. Byv lected by a lens 2l and projected' upon the photothe use of this device, a particularly wide range cathode 22 of an electron multiplier 23. of variations is obtainable while maintaining The electron multiplier is of the type shown in a linear relationship between thev control voltthe above-mentioned copending U. S. applicaage variations and the amplified signal output. tion Serial No. 332,632, wherein its function and Such an electron multiplier for the normal reoperation are described indetail. In brief. the production of sound records is disclosed and 50 electron multiplier has the photocathode vi2, a claimed in copending U. S. application Serial No. plurality 0f dynodes 25. 26, 21,18, 29, 3U and 3l 332,632, led May 1, 1940. and a collector 32. Graduated voltages are im- Although the present'invention is described as pressed upon the series of dynodes and collecembodied in a sound reproducing system, it is to tor from potentiometer resistors 34, the operatbeunderstood that the system is also suitable for ing voltage being supplied from a power supply 35. Connected between the power supply 35 and the collector 32 is a power amplifier 36 which relationship is varied, however, by the remaindery of the system, which will now be described.

As the film passes over the roller Il, a beam of light ,from a light source 40 is projected on the control track 8 after passing through collective lens 4I, slit 42 of a mask 43 and projection lens 44. The emergent vlight is then projected by a lens 45 upon a photoelectric cell 46. It will be noted that the slit 42 is considerably wider or higher than the slit l1. This provides the control track reproducing system with increased efficiency and attenuates the harmonic components of the 96 carrier frequency. The output of the cell 46 is impressed upon a rectifier-amplifier combination 41, then on a timing circuit 48 and then on dynode 21- of the electron multiplier 23. A variable tap coupling resistor 49 is employed for properly coupling the photocell 46 `to the electron multiplier circuit, the voltage developed across the coupling resistor 49 being proportional to the average value of the light on the photocell 46.

In operation of the above-described circuit.`

the electron multiplier 23 detects and amplifles the light passing through the sound track 6 of the film 5, the amplified energy being impressed upon the amplier 36 and reproduced by the loudspeaker 31. In normal operation, the output energy variations will be proportional to the light variations impressed on the photocathode 22. However, this proportionality is varied by the voltage variations impressed on dynode 21.

These voltage variations are obtained from the reproducing system 40-48 which reproduces the control track positioned intermediate the sprocket holes, although it is to be understood that this control track may be a track similar to sound track 6 and may be on a second film or other sound recording medium. 'I'he two tracks have been so positioned on the film that corresponding points'are longitudinally displaced for convenience in reproduction.

The control track system is one wherein the sprocket holes are advanced at a speed of 96 per second, which produces a carrier frequency modulated by the Varying opacity of theA area be- `ltween the sprocket holes as described in detail in the above-identified application. Thus, the amplifier-and-rectier 41 detects the modulated -carrier while the timing circuit 48 controls the rate at which the variations in gain are increased and decreased so that the minimum amount of distortion is introduced at these points. vAlthough the control track record may be recorded so that the variations in density and consequent light variations are at a predeterr mined rate to introduce the minimum amount of distortion, asdisclosed and claimed in applicants copending U. S. 'application- Serial No.

366,590 filed Nov. `22, 1940, it may be desirable' to further control the rate of change in voltage on the multiplier to insure optimum operating conditions. y

Although an individual light source is shown for each film track, a split beam system with a single light source may be employed. Furthermore, the stabilizing features disclosed .in the above-mentioned copending application Serial No. 332,632 may be embodied in the circuit, thus providing a more stable system than heretofore known.

I claim as my invention:

l. Motion picture apparatus comprising means for producing a light beam, means for modulatng said light beam in accordance with sounds to be reproduced, a photoelectric electron multiplier responsive to said modulated light beam and provided with a photoelectric cathode, a plurality of multiplying electrodes and a collecting electrode connected to the output circuit, a source of power supply connected to the electrodes of said multiplier, a second light beam, means for modulating said second beam, and a photocell responsive to said second modulated light beam and connected to said power supply and to one of said multiplying electrodes for varying the output of said electron multiplier irrespective of the modulations of said firstmentioned light beam.

2.'A sound reproducer in accordance with claim l in which said first modulating means includes a film sound track and said second modulating means includes a film control track.

3. In combination with an electron multiplier having a cathode, a collector and a plurality of intermediate dynodes, a source of potential connected to said collector,-said cathode and said dynodes, one of said dynodes being connected to said source of potential through an amplifierrectifier circuit, and a photoelectric cell in the input circuit of said amplifier-rectifier, the variations in light impressed on said photocell varying the potential on said one dynode.

4. A sound reproducing system comprising a -sound track on a film, a control track on said film, means for modulating a light beam inl accordance with said sound track, means for modulating a light beam in accordance with said control track, an electron multiplier having a photocathode, a plurality of dynodes and a collector, a reproducer connected to said collector, means for impressing the light modulated by said sound track on said photocathode, a photoelectric cell connected to one of said plurality of dynodes, and means forv impressing the light modulated by said control track on said photoelectric cell.

5. A reproducing' system in accordance with claim 4 in which an amplifier-rectifier and timing circuit is connected intermediate said photoelectric cell and said one dynode.V

6. A system for expanding the reproduction of a film sound track record comprising means for generating a light beam, means for modulating said light beam-with said sound record, an

electron multiplier for translating said light of predetermined variations in amplitude com-' prising means for translating the amplitude variations of said vsound record into voltage vari-V ations and increasing said voltage variations in a series of electronic steps, said means including an electron multiplier having a photocathode and a plurality of dynodes, means for translating said control record into voltage variations corresponding therewith, said last-mentioned means including a source of light and a photocell, and means for impressing the output of said photocell on one of said dynodes for varying the voltage variations of one of said electronic steps by said control record variations.

8. A system for controlling the reproduced amplitudes of a sound record by a control record comprising means for translating the variations of said sound record into voltage variations and increasing said voltage variations in a plurality of substantially equal electronic steps, said means including an electron multiplier having a photocathode and a plurality of dynodes, means for translating said control record into voltage variations corresponding therewith, said last-mentioned means including a source of light and a photosensitive device, and means for connecting the output circuit of said photosensitive device to one of said dynodes for varying one of said electronic steps of sound track voltage' variations, and means connected intermediate said v device and said one dynode for varying the rate of change of said variations.

9. A sound record expansion system comprising va film having thereon a sound track and a control track disposed intermediate the sprocket holes of said lm, an electron multiplier having a photocathode, a plurality oi dynodes and a collector, a sound reproducer connected to said collector, means for modulating a light beam with the sound record on said lm, means for impressing said modulated light upon the photocathode of said electron multiplier, a photoelectric cell, means for modulating a second light beam by said control track and the sprocket holes of said film for impression on said photoelectric cell, means ing the output of said photoelectric cell, and means for impressing the output of said rectifier on one of Vsaid dynodes for varying the amplication of the detected sound record irrespective of the normal `variation of said sound record.

10. A sound recording system in accordance with claim 9 in which a timing circuit is interposed between said rectifier and said dynode for varying the rate of change of the variations in amplitude of said sound record. Y 1 CECIL N. BATSEL.

for amplifying and rectify-l 

